The disclosed embodiments relate to a transmission arrangement for a tomograph. The disclosed embodiments may be used in magnetic resonance tomography, such as for the wireless energy supply of local coil systems.
In a tomograph examination, a patient is positioned on a couch in a cylindrical measurement area of the tomograph. A strong magnetic field is applied in the measurement area. The magnetic field has a gradient as a result of the excitation of a plurality of gradient coils. The nuclear spin of atoms is aligned by the magnetic field. Disposed within the tomograph is a transmission antenna arrangement, such as a whole body transmission antenna arrangement, e.g., a birdcage antenna, for emitting magnetic resonance radio-frequency pulses to excite the atoms. The birdcage antenna is operated with a magnetic resonance (MR) excitation frequency.
To receive the MR signals from the atoms during an MR examination, local coils are used to receive the pulses upon the relaxation of the nuclear spins. Different materials exhibit different relaxation behavior. Therefore, a conclusion about the interior of the patient's body may be drawn based on the relaxation behavior. The local coils are often combined in assemblies (called “local coil systems” hereinafter) and in each case have reception antenna elements, e.g., in the form of conductor loops. The received MR signals are also preamplified in the local coil and conducted out of the central region of the MR installation via cables. The MR signals are fed to a shielded receiver of an MR signal processing device, in which the received signals are then digitized and processed further. In many examinations, a multiplicity of local coils are arranged on the patient to cover entire regions of the patient's body.
The operation of MR systems is described e.g. in “Imaging Systems for Medical Diagnostics”, Arnulf Oppelt, Publicis Corporate Publishing, ISBN 3-89578-226-2, 2006.
Energy is provided for preprocessing, such as preamplification and, if appropriate, digitization and coding, of the MR signals in the local coil system. The energy may be supplied via a cable, but a cable is undesirable because the cable cannot easily be guided (e.g., led) from the patient couch to the evaluation device. The cable is also regarded as an annoyance by operational personnel and by the patient. Further, the cable is fed loosely because the patient couch is moved together with the patient and the local coil mat.
The energy may also be supplied wirelessly via radio with a linearly polarized energy transmission antenna in the couch and an energy reception antenna coupled to the electronic circuit. However, this approach involves a couch with a complex configuration. Furthermore, the energy transmission antenna supplies maximum power in only one position of the energy reception antenna.
Energy is also supplied via radio with an energy transmission antenna as an additional insert for the MR tomograph and a matching energy reception antenna coupled to the electronic circuit. However, this arrangement is disadvantageous because, for example, the arrangement decreases the internal radius of the MR tomograph.
DE 10 2011 076 918 A1 discloses a local coil system, a transmission device, a magnetic resonance system and a method for wireless energy transfer to a local coil system. The local coil system is provided for an MR system for detecting MR signals with an energy reception antenna that inductively receives energy for the local coil system from a magnetic field that changes over time. The energy reception antenna is tunable or tuned to an energy transfer frequency lower than an MR excitation frequency or Larmor frequency of the MR signals to be detected, and higher than approximately 20 kHz. The transmission device is provided for an MR system and is configured to transmit energy to a local coil system via an energy transmission antenna that emits a magnetic field that changes over time and that has a predetermined energy transfer frequency. An oscillator device is coupled to the energy transmission antenna and generates a signal for driving the energy transmission antenna. The signal has an energy transfer frequency lower than a Larmor frequency of MR signals to be detected via the local coil system, and higher than approximately 20 kHz. The energy transmission antenna may be formed integrally with the whole body coil or around the whole body coil. The transmission device either is relatively voluminous or involves a complex excitation circuit.